POSTTRANSCRIPTIONAL REGULATION OF BOVINE PARATHYROID-HORMONE SYNTHESIS

Incubation of bovine parathyroid cells for 48 h in 0.4 mmol calcium/l had no significant effect on steady-state preproparathyroid hormone (preproPTH) mRNA levels when compared with cells incubated in 1.0 mmol calcium/l, but low calcium concentrations increased the membrane-bound polysomal content of preproPTH mRNA by 200 +/- 16% (mean +/- S.D.). No preproPTH mRNA was detected on free polysomes. Actinomycin D (5 and 10 mug/ml) had no effect on steady-state preproPTH mRNA levels measured in dot-blot assays after 24 h, but reduced levels in cells incubated in 1.0 mmol calcium/l to 54 +/- 16% and 39 +/- 12% of control values respectively after 48 h of incubation. Similarly, in cells incubated in 0.4 mmol calcium/l, actinomycin d (5 and 10 mug/ml) reduced steady-state preproPTH mRNA levels to 57 +/- 13% and 45 +/- 5% of control values respectively. Actinomycin D did not prevent the rise in polysomal content of preproPTH mRNA induced in cells by incubation in 0.4 mmol calcium/l, but increased polysomal content in cells incubated in 0.4 and 1.0 mmol calcium/l by 159 +/- 9% and 164 +/- 13% respectively after 48 h. These results demonstrate post-transcriptional regulation of PTH synthesis in cultured bovine parathyroid cells, and suggest that this control involves a protein which may be calcium-sensitive.